We have found an early sign of pathological brain processes in a subgroup of highly functioning elderly Ss. These Ss performed poorly on a form-board test (Tactual Performance Test - TPT). Degree on TPT impairment in 1977 predicted decline in aspects of Performance IQ from 1977 to 1981. Ss pattern of performance on other tests suggests that the deficit is spatial in nature rather than primarily a psychomotor, memory or learning defect. Impairment on visuo-spatial tasks is one of the most frequent concommitants of normal and pathological aging. A better understanding of the mechanisms underlying the impaired TPT performance will contribute to an understanding of basic aging processes. Such new understanding should ultimately have clinical value. The specific goals of this proposal are threefold: 1) to elucidate the specific impaired functions underlying the spatial processing deficit; 2) to localize the brain region(s) involved in the deficit using probe event-related-potentials (ERPs); and 3) to evaluate the clinical significance of this phenomena through study of highly functioning elderly, average community resident elderly, primary degenerative dementia, multi-infarct dementia, and well functioning younger subject groups. We will use various visuo-spatial and tactile spatial tasks involving both unilateral and bilateral simultaneous presentation of stimuli to pinpoint the functions involved in the deficit. Probe ERPs will be recorded during performance of the spatial tasks to help determine the brain region(s) implicated in the deficit. A cross visual field backward masking paradigm will be used to study both speed and integrity of information transfer between hemispheres; determining whether impairments in these processes are related to the spatial processing deficit.